Pressure-sensitive adhesives (PSAs) are well known and are used in a variety of industrial, consumer and medical applications. The term “pressure-sensitive adhesive” is generally used to designate adhesive materials that will stick to a surface when pressed with simple hand pressure and that have sufficient internal strength that the same can be removed from the surface to which they have been adhered without substantial portions of the adhesive separating from the main adhesive mass. Because of their tackiness, pressure-sensitive adhesives are generally difficult to use for bonding an object coated with the pressure-sensitive adhesive to a substrate whenever it is desired to position the object relative to the substrate by sliding it while the two are in adhesive contact (e.g., mounting a photograph in a scrapbook).
Various known methods for providing such positionability by sliding include placement of particles on the surface of the pressure-sensitive adhesive, and disposing the pressure-sensitive adhesive within recesses in the surface of the object to be adhered. In both cases, the pressure-sensitive adhesive remains physically separated from the surface of the substrate to be bonded until pressure is applied. However, in the normal course of handling such objects, sufficient pressure may be inadvertently applied to such objects (e.g., if they are large and unwieldy) that they become adhered to the substrate before they are properly positioned.
In contrast, hot melt adhesives typically have essentially no adhesive characteristics until heated to their melting point, at which temperature they flow and adhere readily to other surfaces on contact. As the adhesive flows, it typically penetrates any porous materials (e.g., bricks, fabrics, wood) that it contacts to form mechanical entanglements upon cooling to room temperature. With smooth nonporous surfaces, mechanical entanglement is not generally possible, and after the adhesive cools the resultant bond is typically poor. Thus, hot melt adhesives are normally used to form permanent adhesive bonds to porous materials and not to smooth nonporous surfaces.
It would be desirable to have a new adhesive and method for adhering an object to a substrate, including a smooth substrate, which new adhesive and method allow the object to be positioned relative to the substrate by sliding without accidental adhesion occurring before the object is correctly positioned.